In order to investigate the immunological damage in rat immunized with AT1-receptor peptide, 18 male Wistar rats were divided into two groups: immunized-group (n=12), each rat was immunized with 150 μg AT 1-receptor petide coupled to bovine serum albumin, together with Freund’s adjuvant. Control group (n=6), sham-immunized, “immunized liquid” was same as immunized-group except AT1-receptor peptide. Systolic blood pressure (SBP) was measured by using the tail-cuff technique, antibody against AT1-receptor peptide detected by using ELISA method, and left ventricular myocardium and renal cortex sections were observed under light and electron microscopy. There was no significant difference in SBP and light microscopic observation of the tissue sections between the immunized-group and control group. The O.D. value of anti-AT1-receptor peptide antiserum was significantly higher in the immunized-group than in the rats before immunization and control group (P<0.01). Positive rate in the immunized-group was 100 %, while 0 % in the control group. Ultramicroscopic morphology showed potential myocardial injury, including: increase in number of mitochondria, swelling of many mitochondria with reduction in number or absence of their cristae and cristolysis, disorder of the cardiac myofibrils, and myofibrillar disruption and myocytolysis. And lysosomes were increased in renal tubular epithelia. The AT1-receptor peptide could induce to generate the antibody against AT1-receptor peptide and lead to myocardial and renal damage in rats. In order to investigate the immunological damage in rat immunized with AT1-receptor peptide, 18 male Wistar rats were divided into two groups: immunized-group (n = 12), each rat was immunized with 150 μg AT1-receptor petide coupled to bovine Serum albumin, together with Freund’s adjuvant. Control group (n = 6), sham-immunized, “immunized liquid” was the same as immunized-group except AT1-receptor peptide. Systolic blood pressure (SBP) was measured by using the tail -cuff technique, antibody against AT1-receptor peptide detected by using ELISA method, and left ventricular myocardium and renal cortex sections were observed under light and electron microscopy. There was no significant difference in SBP and light microscopic observation of the tissue sections between the immunized -group and control group. The OD value of anti-AT1-receptor peptide antiserum was significantly higher in the immunized-group than in rats before immunization and control group (P <0.01). Positive rate in the im munized-group was 100%, while 0% in the control group. Ultramicroscopic morphology showed potential myocardial injury, including: increase in number of mitochondria, swelling of many mitochondria with reduction in number or absence of their cristae and cristolysis, disorder of the cardiac Myofibrils, and myofibrillar disruption and myocytolysis. And lysosomes were increased in renal tubular epithelia. The AT1-receptor peptide could induce to generate the antibody against AT1-receptor peptide and lead to myocardial and renal damage in rats.